TESTS FOR CHEMICAL REACTIVITY BETWEEN ALKALIES AND AGGREGATE: FURTHER INVESTIGATION OF THE MORTAR-BAR TEST
RESULTS ARE PRESENTED OF AN INVESTIGATION TO DETERMINE THE EFFECT OF THE DIFFERENCES BETWEEN THE CORPS OF ENGINEERS MORTAR-BAR METHOD AND AMERICAN SOCIETY FOR TESTING MATERIALS MORTAR-BAR METHOD FOR DETERMINING ALKALI-AGGREGATE REACTIVITY. THE PRINCIPAL DIFFERENCES BETWEEN THE METHODS ARE: (1) THE GRADING OF THE AGGREGATE USED IN THE MORTAR, (2) THE AGE OF THE BARS WHEN THE INITIAL MEASUREMENT IS TAKEN AND (3) THE NUMBER OF TIMES THE BARS ARE MEASURED. THE ASTM GRADING HAS SLIGHTLY LESS PARTICLE SURFACE AREA THAN THE CRD GRADING AND HAS FIFTEEN PERCENT MORE MATERIAL LARGER THAN THE NO. 16 SCREEN. THE TWO METHODS SPECIFY THAT THE TEST BARS BE MEASURED AT DIFFERENT INITIAL AGES AND SUBSEQUENTLY AT DIFFERNET INTERVALS. TEST BARS WERE MADE USING BOTH A HIGH-AND A MEDIUM-ALKALI CEMENT EACH IN COMBINATION WITH PYREX GLASS, A REACTIVE NATURAL SILICA SAND, AND A NONREACTIVE NATURAL SILICA SAND. EACH OF THE SIX CEMENT-AGGREGATE COMBINATIONS WAS TESTED USING THE CRD GRADING AND MEASURING SEQUENCE AND THEN THE ASTM GRADING AND MEASURING SEQUENCE. IN ADDITION, THE BLOTTING PAPER LINERS WERE PLACED IN THE PLASTIC EXPOSURE CONTAINERS, EXTENDING THROUGH THE ONE INCH OF WATER AT THE BOTTOM OF THE CONTAINERS, WHEN THE BARS WERE REMOVED FOR THE SIX-MONTH MEASUREMENTS TO INCREASE THE AREA FROM WHICH WATER VAPOR COULD ESCAPE INTO THE CONTAINER. THIS WAS DONE BECAUSE IT WAS SUSPECTED THAT THE AIR SURROUNDING THE BARS IN THE CONTAINERS WAS NOT OF THE DESIRED RELATIVE HUMIDITY. RESULTS INDICATE THAT THERE WAS A SIGNIFICANT DIFFERENCE IN SOME CASES, BETWEEN THE EXPANSIONS AND MORTAR BARS CONTAINING ASTM GRADED REACTIVE AGGREGATES THAT WERE MEASURED ACCORDING TO THE ASTM SPECIFIED SEQUENCE, AND BARS CONTAINING CRD AGGREGATES THAT WERE MEASURED ACCORDING TO THE CRD SPECIFIED MEASURING SEQUENCE. WHERE THERE WAS A SIGNIFICANT DIFFERENCE, THE ASTM BARS EXPANDED MORE THAN CRD BARS. SUBSEQUENT MEASUREMENT OF BARS AFTER ABSORPTIVE LINERS WERE PLACED IN THE EXPOSURE CONTAINERS SHOWED AN ABRUPT INCREASE IN EXPANSION OF THE BARS IN MOST CASES. IT IS EVIDENT THAT THE AIR SURROUNDING THE BARS IS NOT ALWAYS OF THE DESIRED RELATIVE HUMIDITY WHEN BAR ARE EXPOSED IN PLASTIC CONTAINERS OF THE TYPE PRESCRIBED IN THE CRD METHOD. IT IS RECOMMENDED THAT CRD METHOD BE REVISED TO CONFORM TO ASTM C 227, AND THAT ABSORPTIVE LINERS BE PLACED IN ALL CONTAINERS WHERE THE RELATIVE HUMIDITY INSIDE THE CONTAINER IS QUESTIONABLE.
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Supplemental Notes:
- Tm 6-368, REPT 3, 33 PP, 12 FIG, 5 TAB, 7 REF
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Authors:
- Houston, B J
- Publication Date: 1967-10
Media Info
Subject/Index Terms
- TRT Terms: Absorption; Age; Aggregate gradation; Alkali aggregate reactions; Bars (Building materials); Binders; Chemical reactivity; Expansion; Humidity; Materials tests; Mortar; Silica sands; Specimens; Standardization; Test procedures
- Old TRIS Terms: Mortar bar method; Pyrex
- Subject Areas: Geotechnology; Highways; Materials;
Filing Info
- Accession Number: 00216279
- Record Type: Publication
- Files: TRIS
- Created Date: Mar 22 1994 12:00AM